Yes, there are prior gospels. Here is an excellent reference, The Missing Gospels by Darrell. L. Block. According to history, church leaders destroyed as many gospels as they could find which disagreed with the four selected. The Gospel of Thomas is a prior gospel which was used as a reference for the four gospels. You find "many" Jesus sayings from The Gospel of Thomas in the four NT gospels.
You say "according to history" - What history? Show us the historical documentation. Opinions are a dime a dozen; I can throw around endless names of authors who would say that person is absolutely wrong, so the only way to settle this is to look at the evidence directly for ourselves.
Prior to Nicea, when the church gained government protection; every canon list, book compilation, and early church writing we have all attest to the authenticity of the canon we have as being already known and established by the 2nd century. So your entire premise is impossible: If the canon was already established before Nicea, as we can see in history, then we know that the canon could never have been established by force and destruction.
Show us why there is any historical reason to believe there were gospels that were written prior to the four we have in the Bible.
Even the most unbelieving scholar doesn't try to suggest that the gnostic gospels that have been recovered actually represent 1st century works. Nobody even tries to claim that the entirety of thomas is from prior to the 1st century, but only claims parts of it might be based on agreement with the NT. And even saying that much is a minority view, with no historical proof to back it up - it's just speculation.
Only an extreme minority of revisionist historians even attempt to claim the gospel of thomas served as a source for the Biblical gospels; but it's first mention in history is not until the 3rd century when some church fathers mention it as an example of a false gospel. Again, there's no historical basis for what they claim, it's an unsupported theory that conflicts with what we do know about history - We have ample historical witness from the 2nd century of canon lists, church writers, book compilations, and other documents which all attest to the books we have in the NT today, and none of them can give even the faintest hope of attestation to the gospel of thomas.
Most of the gospel of thomas is just requoting NT sources, and the rest is mostly generic nonsense that has no witness in the early church or rest of the Bible.
Where are the early church writings that quote from or are in agreement with the generic parable nonsense found in Thomas? I've encountered no examples of it. If Thomas were a genuine 1st century document, we'd expect the material that is unique to it to be reflected in other early church documentation. Even for the authentic gospels, when dealing with material that is unique to those, we find ample reason from both the OT, other NT books, and early church history, to witness to the truth contained in the four gospels. Thomas is isolated in that sense, with no supporting witness beyond what it has just ripped strait of existing gospels.
The contents of the gospel of thomas also contradict what is found in the NT gospels and epistles, as well as what is found in the OT prophets. God does not contradict Himself. Either thomas is right or all of the NT and OT is wrong. That's an impossible claim when the gospel of thomas doesn't predate either of them.
Some disqualifying major contradictions:
Thomas (13): Jesus corrects them for calling Him "master", and says He is not their master.
Bible: Luke 17:14. John 13:13. Jesus does not correct those who call Him master, but affirms they are right to do so. He also says that no one else on earth is to be considered master, or father, or messiah, because their is only one who can be called that (Matthew 23).
Thomas (51). It claims the resurrection of the dead has already happened, and the new world has already come.
Bible: John 11:24, John 6:39, Luke 14:12-14, Luke 18:8, Luke 18:30, Luke 20:35-36, Acts 1:11, Acts of the Apostles 23:6, Acts of the Apostles 24:15, Mark 10:30, Hebrews 2:5, 2 Peter 3:12-14, Revelation 21:2, 2 Peter 3:3-5, 1 Corinthians 6:14, 1 Thessalonians 4:16, 1 Thessalonians 4:13-14, 1 Corinthians 15:51-53, 1 Corinthians 15:30-32, 1 John 3:2, Philippians 3:21, Psalms 17:15, Psalms 71:20, Isaiah 26:19, Isaiah 65:17, Hosea 13:14, Revelation 21:4, Isaiah 65:20.
The resurrection of all from the dead, the establishment of a new order, and eventually the recreation of the earth and heavens, are all linked with the return of Jesus. The gospel of thomas is trying to deny the major hope of the Christian faith by saying that which was promised has already come in full.
Ephesians 1:14, 2 Corinthians 1:22, Acts of the Apostles 26:22-23, Romans 8:23, James 1:18,
Except, we see in the Bible, that what we see with Jesus and the early church is only the first fruits and downpayment of what will later be given in full.
This is pictured in the observance of the first fruits of the harvest in the Levitical feasts God gave for observance. It is also reflected in parables given by Jesus where His church is a bride waiting for the consummation of what was promised to them (An engagement is a promise that will be fulfilled at a later day, to which the bride is usually given a downpayment as proof of their promise).
Thomas (77). A pantheistic view of Jesus not found in the Bible.
Thomas (114) Simon Peter said to him, "Let Mary leave us, for women are not worthy of life."
Jesus said, "I myself shall lead her in order to make her male, so that she too may become a living spirit resembling you males. For every woman who will make herself male will enter the kingdom of heaven."
Jesus talked a lot about entering the Kingdom of Heaven, and none of it ever suggested anything have to do with distinctions of sex.
The gospel of thomas fits the pattern one would expect to find of a document that was forged at a later date with the intention of fooling people who are familiar with the authentic historical gospels. Similar to the fabricated epistle of laodicea, where most of the document is spent restating what is found elsewhere or making generic irrelevant statements. The only difference between these two: Laodicea was not written with the intent of spreading lies that contradict the authentic NT documents, but was interested in merely being passed off as historically authentic when it was not. Thomas, in contrast, is clearly written with the intent of putting forth unbiblical lies as truth, because there are several instances where it tries to strike at the heart of foundational issues of who Jesus is, how salvation is achieved, and the prophetic hope we have of Jesus's return - all hidden in the midst of generic statements and Biblical restatements that are meant to give the illusion of authenticity to someone who is not well versed in the scriptures (and to that end, it has succeeded in fooling some modern people who don't know the Bible well or believe it's contents).
